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Article Figures & SI

Figures

Distribution of floating materials from satellite images. (A) Oil from Deepwater Horizon spill seen in a sunglint image. (B) Cyanobacteria bloom in the central Baltic Sea (57.7°N, 20.7°E, water depth 135 m). Dark line is the wake of a ship.

Evolution of the drifter array. (A–F) Drifter positions at selected times, a subset of the online animation (SI Animation of Drifter Evolution). (E, Inset) Detail of a 60-m-wide cluster of 127 drifters, colored magenta, at its smallest. Each panel is centered on these magenta drifters; nearly all of the other drifters exit the frame by F. Gray lines show 7,500-s-long “tails” of drifter motion. (G) Distribution of drifter pair separations as a function of time (gray shading indicates the number of pairs in each of the 100 logarithmically spaced bins; larger numbers are darker). RMS pair separation (red) and times of A–F (blue lines) are shown. (H) Same, but for separations of drifters from the center of drifter clusters (SI Drifter Cluster Analysis). (I) Same, but for separations between the centers of the drifter clusters. Grayscale has been adjusted to compensate for the different numbers of pairs in different panels.

A convergent submesoscale structure. (A) Surface density (colored dots) from ship sections across the drifter array and drifter trajectories (gray) during the same time period (black dot marks trajectory end). Positions are plotted in a coordinate system moving with the cyclonic eddy (eastward at 0.13 m s−1, southward at 0.05 m s−1). A section is highlighted in red. (B) Potential density (colors and contours) along the highlighted section. Data are averaged over 3 m vertically and 1 km horizontally. Red dots indicate surface positions of individual profiles. Large gray circle, duplicated in other panels, marks the location of densest surface water on yearday ∼42.5. (C) Vorticity/f (colored ellipses) computed (SI Estimating Vorticity and Divergence from Drifter Data) from drifters on yearday 42.522 and drifter trajectories during the previous 5,000 s (gray line ending at black dot). Ellipse shape shows the spatial distribution of drifters; only data with ellipses with a major to minor axis ratio less than 5 are used. (D) Divergence/f at the same time. (E and F) Same as C and D but at yearday 43.772.

Sinking of water at the front. (A) Surface density colored and contoured using same color map as in Fig. 5. Thin lines show ship survey lines; yellow lines indicate the section plotted in B; circles show stations. Mapping uses objective analysis with a 1.2-km Gaussian correlation function. Black dots show drifter positions with 5,200-s tails, the duration of the survey. (B) Section of potential density using all data along yellow tracks (SI Float Navigation). Small white dots show profile locations. Data are smoothed with 2 m vertical and 500 m horizontal scales. (C) Sketch of the Lagrangian float and vertical velocity (colors) computed from its data. Float was deployed at the location of the top star in A and recovered at the bottom star. Estimated trajectory (SI Float Navigation) is shown by the red lines in A and B and marked by white symbols common to all panels. Solid lines are more certain than dashed ones. Horizontal arrows in B indicate uncertainty in the cross-frontal position. Vertical velocity in C is computed from the float’s vertical motion (colored line) and from the upward-looking ADCP (colors and contours). Long arrows in each panel indicate the sense of circulation.

Data supplements

Supporting Information

Download Movie_S01 (MOV) -
Trajectories of LASER drifters used in this paper. Each circle is the position of
a drifter as in Fig. 4 A–F at the yearday of 2016 noted at the top of the figure.
Trajectory tails of 12,500 s are plotted in gray. Positions are given in kilometers
from 29°N, 88.25°W. Magenta dots will form a tight cluster by the end of the animation.
Open dots will not join the cluster. The frame is centered on the center of mass of
the magenta dots and shifts with each frame, but the scaling remains constant. Annotated
key is shown in Fig. S5.

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